Inductive filters and methods of fabrication thereof

ABSTRACT

A series of plated through hole (PTH) vias are interconnected by traces that alternate between a top surface and a bottom surface of a dielectric board. The PTH vias in the series can be positioned to create a collinear inductive filter, a coil-type inductive filter, or a transformer. Multiple, electrically isolated series of interconnected PTH vias can be used as a multi-phase inductive filter in one embodiment. In another embodiment, multiple series of interconnected PTH vias are electrically connected by a linking portion of conductive material, resulting in a low-resistance inductive filter. Ferromagnetic material patterns can be embedded in the dielectric board to enhance the inductive characteristics of the interconnected via structures. In one embodiment, a closed-end pattern is provided with two series of interconnected vias coiling around the pattern, resulting in an embedded transformer structure. A method of producing an interconnected series of PTH vias includes providing a dielectric board having a series of holes. In some embodiments, the board includes an embedded ferromagnetic material pattern. The holes and the top and bottom surface of the dielectric board have a conductive material thereupon. Portions of the conductive material are selectively removed, resulting in the embedded inductive filter and/or transformer structure.

This application is a divisional of U.S. application Ser. No.09/473,353, filed Dec. 28, 1999, now issued as U.S. Pat. No. 6,493,861.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to microelectronic structuresand fabrication methods, and more particularly to microelectronicstructures having inductive characteristics and methods of fabricatingthe same.

BACKGROUND OF THE INVENTION

A requirement of most electronic systems is a regulated source of directcurrent (DC) voltage. Whether the DC power originates with a battery orhas been converted from alternating current (AC) power, a voltageregulator circuit is usually required to provide a steady DC voltage.

FIG. 1 illustrates a simple power supply circuit 100 that includes avoltage regulator. In power supply circuit 100, the voltage provided byAC voltage source 110 is increased or decreased by transformer 112 to avoltage having a magnitude that is required by the load. The transformedvoltage passes through rectifier 114, which is a set of diodes inFIG. 1. The voltage is then filtered by capacitive filter 116. Theresulting voltage is regulated by voltage regulator 118, which can be adiscrete component circuit or an integrated circuit voltage regulator.Either way, the output voltage is filtered through inductive filter 120.The filtered voltage is then supplied to load 122, which could be, forexample, an integrated circuit such as a microprocessor.

To supply voltage to an integrated circuit, transformer 112, rectifier114, capacitive filter 116, and voltage regulator 118 are typicallyconsolidated into a voltage regulator module (VRM), which is a discretecomponent that is mounted on a printed circuit (PC) board. Inductivefilter 120 typically is a separate component, due to the relativelylarge size of the inductor.

FIG. 2 illustrates a VRM 202 and an inductive filter 204 located on a PCboard 206 of a computer system in accordance with the prior art. Tosupply power to an integrated circuit, electrical current first travelsfrom the VRM 202 through the inductive filter 204. The current thentravels through traces (not shown) in PC board 206, and up throughsocket 208 to pins 210 of an integrated circuit (IC) package 212 Thecurrent continues along traces (not shown) in IC package 212 toconnections 214. Connections 214 make electrical contact with pads (notshown) on the integrated circuit 216.

The scale and/or location of pins 210 on an IC package 212 may bedifferent from the scale and/or location of pin holes on the socket 208.Thus, in some systems, an interposer (not shown) exists between the ICpackage 212 and the socket 208. The interposer essentially is a smallprinted circuit board that provides a dimensional interface between theIC package pins 210 and the pin holes of the socket 208. When aninterposer is present, the supplied current must also travel through theinterposer to reach the integrated circuit.

A voltage drop occurs between VRM 202 and integrated circuit 216, due tolosses along the path between VRM 202 and integrated circuit 216. Allother things being equal, the farther the distance between VRM 202 andintegrated circuit 216, the larger the voltage drop. At relatively lowvoltages, this voltage drop is a tolerable effect that is compensatedfor by providing a VRM that supplies a higher voltage than is actuallyneeded by the integrated circuit. A negative side effect of thisstrategy, however, is that the VRM may need to be larger than necessary,and power is inefficiently consumed.

Technological advancements in integrated circuit technologies aredriving frequency requirements higher, and driving voltages and voltagemargins lower. Therefore, it is desirable to reduce the inefficientpower consumption caused by the voltage drop between the VRM and theintegrated circuit. This reduction in voltage drop can be achieved bymoving the VRM and inductive filter as close as possible to theintegrated circuit. However, the proximity of the VRM and inductivefilter to the integrated circuit is limited by the fact that the VRM andinductive filter must be located on the PC board in prior art systems.

For the reasons stated above and for other reasons stated below, whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art fora circuit configuration enabling a VRM and inductive filter to be placedcloser to the integrated circuit than is possible in prior art systems.

SUMMARY OF THE INVENTION

In one embodiment, a method for forming an interconnected series ofplated through hole (PTH) vias begins by providing a dielectric boardwith a series of PTH vias formed therein. The PTH vias are electricallyconnected on a top surface and a bottom surface of the dielectric boardby a conductive material. Portions of the conductive material are thenselectively removed so that adjacent PTH vias are electrically connectedby a trace of the conductive material on either the top surface or thebottom surface. The adjacent PTH vias in the series alternate betweenbeing electrically connected by a trace on the top surface orelectrically connected by a trace on the bottom surface.

In another embodiment, a series of interconnected PTH vias forms aninductive filter that includes a dielectric board having a top surfaceand a bottom surface, and a series of PTH vias formed in the dielectricboard. Conductive material traces exist on the top surface and thebottom surface that electrically connect the PTH vias. Adjacent PTH viasare electrically connected by a trace on either the top surface or thebottom surface, and the adjacent PTH vias in the series alternatebetween being electrically connected by a trace on the top surface orelectrically connected by a trace on the bottom surface.

In yet another embodiment, two series of interconnected PTH vias forms atransformer that includes a dielectric board having a top surface and abottom surface. A ferromagnetic material pattern forming a core isembedded in the dielectric board, and has a closed-end shape. A firstseries of interconnected PTH vias is formed in the dielectric board. ThePTH vias in the first series and traces of conductive material on thetop surface and bottom surface form a first coil-like structure thatwinds around the core. A second series of interconnected PTH vias isalso formed in the dielectric board. The PTH vias in the second seriesand additional traces of conductive material on the top surface andbottom surface form a second coil-like structure that winds around thecore. The first coil-like structure, the second coil-like structure, andthe coil form the transformer.

One embodiment can be, an integrated circuit package includes a packagehaving a first series of PTH vias that provide electrical connectionsbetween a top surface of the package and a bottom surface of thepackage. The PTH vias in the first series are electrically connected byconductive material traces on the top surface and the bottom surface,and adjacent PTH vias in the first series alternate between beingelectrically connected by a trace on the top surface or electricallyconnected by a trace on the bottom surface. The integrated circuitpackage also includes an integrated circuit located on the top surfaceof the package. The integrated circuit contains a circuit which iselectrically connected to a PTH via of the first series.

An interposer designed to provide a dimensional interface between anintegrated circuit package and a printed circuit board includes a firstseries of PTH vias that provide electrical connections between a topsurface of the package and a bottom surface of the package is providedin one embodiment. The interposer also includes conductive materialtraces on the top surface and the bottom surface that electricallyconnect the PTH vias in the first series, where adjacent PTH vias in thefirst series alternate between being electrically connected by a traceon the top surface or electrically connected by a trace on the bottomsurface.

A computer system embodiment is positioned on a printed circuit boardincludes a bus, a memory coupled to the bus, and an integrated circuitpackage coupled to the bus. The integrated circuit package includes apackage having a first series of PTH vias that provide electricalconnections between a top surface of the package and a bottom surface ofthe package. The PTH vias in the first series are electrically connectedby conductive material traces on the top surface and the bottom surface,and adjacent PTH vias in the first series alternate between beingelectrically connected by a trace on the top surface or electricallyconnected by a trace on the bottom surface. The integrated circuitpackage also includes a microprocessor located on the top surface of thepackage, the microprocessor containing a circuit which is electricallyconnected to a PTH via of the series of PTH vias.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a simple power supply circuit in accordance with theprior art;

FIG. 2 illustrates a voltage regulator module and an inductive filterlocated on a mother board of a computer system in accordance with theprior art;

FIG. 3 illustrates a flowchart of a method for fabricating one or moreseries of interconnected plated through hole (PTH) vias in accordancewith one embodiment of the present invention;

FIGS. 4–8 are schematic cross sections illustrating various stages offabricating one or more series of interconnected PTH vias in accordancewith one embodiment of the present invention;

FIG. 9 illustrates an electrical circuit that simulates the electricalcharacteristics of the inductive filter illustrated in FIG. 8;

FIG. 10 illustrates a top view of a single-phase, collinear inductivefilter in accordance with one embodiment of the present invention;

FIG. 11 illustrates a top view of a multi-phase, collinear inductivefilter in accordance with one embodiment of the present invention;

FIG. 12 illustrates an electrical circuit that simulates the electricalcharacteristics of the inductive filter illustrated in FIG. 11;

FIG. 13 illustrates a top view of a single-phase, coil-type inductivefilter in accordance with one embodiment of the present invention;

FIG. 14 illustrates a top view of a multi-phase, coil-type inductivefilter in accordance with one embodiment of the present invention;

FIG. 15 illustrates a top view of a low-resistance, single-phase,collinear inductive filter in accordance with one embodiment of thepresent invention;

FIG. 16 illustrates a top view of a low-resistance, single-phase,coil-type inductive filter in accordance with one embodiment of thepresent invention;

FIG. 17 illustrates a top view of a low-resistance, multi-phase,collinear inductive filter in accordance with one embodiment of thepresent invention;

FIG. 18 illustrates a top view of a low-resistance, multi-phase,coil-type inductive filter in accordance with one embodiment of thepresent invention;

FIG. 19 illustrates a flowchart of a method for providing a dielectricboard with an embedded ferromagnetic material pattern in accordance withone embodiment of the present invention;

FIGS. 20–27 are schematic cross sections and top views illustratingvarious stages of fabricating an embedded filter or transformer inaccordance with one embodiment of the present invention;

FIG. 28 illustrates a top view of a single-phase, coil-type inductivefilter with a ferromagnetic core in accordance with one embodiment ofthe present invention;

FIG. 29 illustrates a top view of a transformer in accordance with oneembodiment of the present invention;

FIG. 30 illustrates an electrical circuit that simulates the electricalcharacteristics of the transformer illustrated in FIG. 29;

FIG. 31 illustrates the incorporation of one or more embedded series ofinterconnected PTH vias in an integrated circuit package in accordancewith one embodiment of the present invention;

FIG. 32 illustrates the incorporation of one or more embedded series ofinterconnected PTH vias in an interposer and/or integrated circuitpackage in accordance with one embodiment of the present invention; and

FIG. 33 illustrates a general purpose computer system in accordance withone embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An apparatus of the present invention includes one or more series ofinterconnected plated through hole (PTH) vias that function as aninductive filter or transformer. These series of PTH vias are embeddedin a semiconductor package or interposer. When serving the function ofan embedded inductive filter, the interconnected PTH via structureenables the discrete inductive filter (e.g., filter 204, FIG. 2) to bereplaced or substantially reduced in size. By eliminating or reducingthe size of the inductive filter, it becomes possible to place a voltageregulator module (VRM) on an integrated circuit (IC) package orinterposer. The closer proximity of the VRM to the integrated circuitresults in less voltage drop and a much more efficient power deliverysystem.

When serving the function of an embedded transformer, the interconnectedPTH via structure enables the transformer portion (e.g., transformer112, FIG. 1) of the VRM to be removed from the VRM, thus reducing thesize of the VRM. This also facilitates placement of the VRM onto aninterposer and/or IC package.

FIGS. 3–30 illustrate the fabrication of various embodiments ofinterconnected series of PTH vias. FIGS. 31 and 32 illustrate theincorporation of these PTH via structures in an IC package andinterposer. Finally, FIG. 33 illustrates a general purpose computersystem that includes one or more series of interconnected PTH vias.

FIG. 3 illustrates a flowchart of a method for fabricating one or moreseries of interconnected PTH vias in accordance with one embodiment ofthe present invention. In order to best describe the method offabricating, FIG. 3 should be viewed in conjunction with FIGS. 4–8,which are schematic cross sections illustrating various stages offabricating one or more series of interconnected PTH vias in accordancewith one embodiment of the present invention.

The method begins, in block 302, by providing a dielectric board 402(FIG. 4), which has a top surface 404 and a bottom surface 406. In oneembodiment, dielectric board 402 is an organic substrate, such as anepoxy material. For example, standard printed circuit board materialssuch as FR-4 epoxy-glass, polymide-glass, benzocyclobutene, Teflon,other epoxy resins, or the like could be used in various embodiments. Inalternate embodiments, dielectric board 402 could consist of aninorganic substance, such as ceramic, for example.

Both the top and bottom surfaces 404, 406 of dielectric board 402 aresubstantially horizontal. In various embodiments, the thickness ofdielectric board 402 is within a range of 600–1000 microns, with itbeing approximately 800 microns in one embodiment. Dielectric board 402could be thicker or thinner than this range in other embodiments.

Referring back to FIG. 3, in block 304, one or more series of holes 502(FIG. 5) are formed through dielectric board 402. In variousembodiments, the diameter of each hole 502 is within a range of 50–150microns, with it being approximately 100 microns in one embodiment. Thisdiameter could be larger or smaller than this range in otherembodiments.

As will be described in more detail below, the series of holes 502 couldbe formed in a substantially collinear manner in one embodiment. Thisorientation will be described in more detail in conjunction with FIG.10, and can be used to provide a collinear inductive filter. In otherembodiments, each hole in the series could be offset from the precedinghole. For example, odd numbered holes in the series could besubstantially collinear with each other. Even numbered holes could alsobe substantially collinear with each other, but they could be formedalong a line that is offset from, but substantially parallel to the linealong which the odd number holes are formed. This orientation will bedescribed in more detail in conjunction with FIG. 13, and can be used toprovide a coil-type inductive filter.

In addition, although only one series of holes 502 is shown in FIG. 5,multiple series of holes could be provided in various alternateembodiments. For example, as will be described in conjunction with FIGS.11, 14, 17, and 18, multiple series of PTH vias could be used to providea multi-phase inductive filter. Alternatively, as will be described inconjunction with FIG. 29, multiple series of holes could be used toprovide an embedded transformer.

Holes 502 are defined by sidewalls 504, which are substantiallyvertical, or orthogonal, to the top and bottom surfaces 404, 406 ofdielectric board 402. In one embodiment, holes 502 are mechanicallydrilled, although holes 502 may also be punched or drilled using a laseror other drilling technologies in various other embodiments. Ifdielectric board 402 is an inorganic substance, such as ceramic, otherhole formation techniques known to those of skill in the art would beused.

Referring back to FIG. 3, in block 306, a conductive material layer 602(FIG. 6) is formed on the sidewalls 504 of holes 502, and on top andbottom surfaces 404, 406 of dielectric board 402. In one embodiment,conductive layer 602 is formed using electroplating techniques, althoughother techniques could be used in other embodiments. For example, ratherthan providing dielectric board without a conductive material in block302, a clad laminate, such as a copper-clad laminate, could be provided,making block 306 unnecessary. In one embodiment, conductive layer 602 isa copper layer, although other conductive metals such as tin, lead,nickel, gold, and palladium, or other materials could be used in otherembodiments.

PTH vias are defined by portions 604 of the conductive layer 602 thatare disposed on sidewalls 504. Other portions 606 of the conductivelayer are horizontally-disposed on the top and bottom surfaces 404, 406of dielectric board 402, resulting in an electrical connection betweeneach PTH via 604 and the horizontally disposed portions 606 of theconductive layer. In various embodiments, the thickness of conductivelayer 602 is within a range of 5–15 microns, with it being approximately10 microns in one embodiment. Conductive layer 602 could be thicker orthinner than that range in other embodiments.

Referring back to FIG. 3, in block 308, holes 502 are substantiallyfilled with a conductive material 702 (FIG. 7). Holes 502 could bescreen-filled, for example, using a paste of conductive material.Conductive material 702 could be copper, for example, although otherconductive materials could be used in various embodiments. In alternateembodiments, holes 502 could be filled with a non-conductive materialsuch as an epoxy fill material, although other non-conductive materialsalso could be used in other embodiments.

In block 310, portions of the conductive material layer on the top andbottom surfaces 404, 406 of the dielectric board 402 are selectivelyremoved, leaving conductive traces 802, 804 (FIG. 8) on the top andbottom surfaces 404, 406. Removal of the portions of conductive materialcould be performed, for example, using a common subtractive technologysuch as a photo or laser imaging and etching process. Other subtractivetechnologies could be used in other embodiments. In still otherembodiments, additive technology could be used to deposit conductivetraces 802. For example, rather than plating and etching top and bottomsurfaces 404, 406, traces 802 could be selectively screened or stenciledusing a conductive paste. After creating conductive traces 802, themethod ends.

The flow of current along the interconnected via structure can be tracedfrom the left side of the structure to the right as follows. First, thecurrent flows along a first trace 802 on the top surface 404 of thedielectric board 402. The current then flows down through PTH via 806,and along a second trace 804 on the bottom surface 406 of the dielectricboard 402. The current then flows up through PTH via 808, and so on, forthe length of the interconnected PTH via structure.

The nonlinear path of the current is similar to the path experienced inan inductor, and thus the PTH via structure shown in FIG. 8 emulates theelectrical properties of an inductor. FIG. 9 illustrates an electricalcircuit that simulates the electrical characteristics of the inductivefilter illustrated in FIG. 8. Circuit 900 includes a resistor 902 inseries with an inductor 904.

The value of resistor 902 depends on the conductive characteristics ofthe conductive material, the cross-sectional area and length of traces802, 804, the diameter and depth of PTH vias 806, 808, and the number ofPTH vias 806, 808 in the structure. Similarly, the value of inductor 904depends on the number and proximity of PTH vias 806, 808 with respect toeach other, and the magnetic permeability of dielectric board 402.

Although six PTH vias 806, 808 are shown in FIG. 8, the number of PTHvias 806, 808 in the inductive filter structure can be varied during thedesign process to adjust the resistance and inductance values. Inaddition, although traces 802, 804 and PTH via sizes and locations areillustrated with specific relative dimensions, the relative dimensionsand locations of the PTH vias and traces, and the magnetic permeabilityof dielectric board 402 can also be varied during the design process toadjust the resistance and inductance values.

Using the structure shown in FIG. 8, current can be filtered in roughlythe same manner as it would be using a discrete inductive filter. Thus,the embedded structure of the present invention can be used in place ofa discrete inductive filter, for example, to filter the output of a VRM.

FIG. 10 illustrates a top view of a single-phase, collinear inductivefilter in accordance with one embodiment of the present invention.Filled PTH vias 1002 are arranged in a substantially collinear manneralong line 1004. In alternate embodiments, PTH vias 1002 could bearranged in a non-collinear manner. Sets of PTH vias are electricallyconnected on the top surface of dielectric board 402 by top traces 1006.The PTH vias are also electrically connected on the bottom surface ofdielectric board 402 by bottom traces 1008, shown in FIG. 10 as dashedlines. Thus, along the top surface and the bottom surface, adjacent PTHvias alternate between being electrically connected and electricallyisolated. If two adjacent PTH vias are electrically connected on onesurface, the same two adjacent PTH vias are electrically isolated on thebottom surface.

The interconnected PTH structure, by itself, provides a single-phaseinductive filter. In order to provide a multi-phase inductive filter,multiple via structures could be used. FIG. 11 illustrates a top view ofa multi-phase, collinear inductive filter in accordance with oneembodiment of the present invention. In the embodiment shown, atwo-phase filter is provided by supplying two series of interconnectedPTH vias. The first series includes PTH vias 1102, that are electricallyconnected by traces 1104 on the top and bottom surfaces of thedielectric board 402. The second series includes PTH vias 1106 that areelectrically connected by traces 1108 on the top and bottom surfaces.

The first series and the second series are electrically isolated fromeach other. Thus, during the selective removal block 310 of theflowchart of FIG. 3, all portions of the conductive material existingbetween the two series are removed from the surfaces of the dielectricboard. The electrical isolation of each series enables each series to beused to filter a different phase of the supplied current.

Each PTH via in a series could be collinear with the other PTH vias inthe series. For example, FIG. 11 illustrates that PTH vias 1102 areformed along line 1110, and PTH vias 1106 are formed along line 1112. Inalternate embodiments, the PTH vias in a series could be non-collinear.Lines 1110 and 1112 could be substantially parallel to each other,although it is not essential that this be the case. In alternateembodiments, lines 1110 and 1112 could be arranged at various angles toeach other.

FIG. 12 illustrates an electrical circuit that simulates the electricalcharacteristics of the inductive filter illustrated in FIG. 11. Thecircuit shown in FIG. 12 is similar to that illustrated in FIG. 9,except that a first series resistor 1202 and inductor 1204 is inparallel with a second series resistor 1206 and inductor 1208. When usedas a multi-phase filter, each resistor/inductor series can be used tocarry a different phase of current. Although only two series are shownin FIGS. 11 and 12, it would be obvious to one of skill in the art basedon the description herein, that three or more series could be used toprovide filtering for three or more phases.

As described previously, the PTH vias in a series of vias could bearranged in a collinear or non-collinear manner. In one embodiment,arrangement of the PTH vias in a non-collinear manner results in acoil-type inductive filter.

FIG. 13 illustrates a top view of a single-phase, coil-type inductivefilter in accordance with one embodiment of the present invention. ThePTH vias 1301, 1302, 1303, 1304, 1305, 1306, 1307, and 1308 in theseries are arranged along two, substantially parallel lines 1310, 1312,which are offset from one another. The odd numbered PTH vias 1301, 1303,1305 and 1307 are substantially collinear with each other along line1310, and the even numbered PTH vias 1302, 1304, 1306, and 1308 aresubstantially collinear with each other along line 1312.

The PTH vias 1301–1308 are electrically connected with each other bytraces 1314, 1316 on the top and bottom surfaces, respectively, of thedielectric board 402. Moving from left to right, electrical currentflowing through the series of vias would flow along a top trace 1314,down through a PTH via 1302, along a bottom trace 1316, up through thenext PTH via 1303, and so on through the series. The current, therefore,follows a roughly spiral-shaped path. This path resembles a coil, andthus the structure illustrated in FIG. 13 emulates a coil-type inductivefilter.

An electrical circuit modeling the electrical characteristics of thestructure in FIG. 13 was shown and described in conjunction with FIG. 9.Variables that affect the values of resistor 902 and inductor 904 arethose listed in conjunction with FIG. 9, but also include the number,tightness, and diameter of “windings” in the PTH via structure, where awinding is comprised of two adjacent PTH vias in the series and a topand bottom trace connected to those vias. For example, three and a halfwindings are illustrated in the PTH via structure of FIG. 13. Inalternate embodiments, more or fewer windings could be included in thePTH via structure. In addition, the relative spacing of the PTH viaswith respect to each other could be altered to adjust the electricalcharacteristics of the inductor.

FIG. 14 illustrates a top view of a multi-phase, coil-type inductivefilter in accordance with one embodiment of the present invention. Inthe embodiment shown, a two-phase filter is provided by supplying twoseries of interconnected PTH vias. The first series includes PTH vias1402, that are electrically connected by traces 1404 on the top andbottom surface of the dielectric board 402. The second series includesPTH vias 1406 that are electrically connected by traces 1408 on the topand bottom surface. The first series and the second series areelectrically isolated from each other, enabling each series to providean inductive filter to a different phase of the supplied current.

PTH vias 1402 are formed along lines 1410, 1412, and PTH vias 1406 areformed along lines 1414, 1416. Accordingly, each series provides acoil-type inductive filter. The set of lines 1410, 1412 could besubstantially parallel to the set of lines 1414, 1416, although it isnot essential that this be the case. In alternate embodiments, line set1410, 1412 and line set 1414, 1416 could be arranged at various anglesto each other.

In order to reduce the resistance of the PTH via structure (e.g., theresistance modeled by resistor 902, FIG. 9), it is possible toeffectively increase the cross-sectional area of traces and PTH vias invarious embodiments of the present invention. This can be accomplishedby electrically connecting multiple series of interconnected PTH vias.

FIG. 15 illustrates a top view of a low-resistance, single-phase,collinear inductive filter in accordance with one embodiment of thepresent invention. Two collinear interconnected PTH via structures areshown, with one structure being defined by traces 1502 and PTH vias 1504along line 1506, and the second structure being defined by traces 1508and PTH vias 1510 along line 1512. Lines 1506 and 1512 could be, but arenot necessarily, substantially parallel.

These PTH via structures are interconnected by a linking portion 1514 ofconductive material that electrically connects at least one PTH via ineach series. This results in a set of multiple interconnected PTH viaseries. Linking portion 1514 could be located on the top surface or thebottom surface of dielectric board 402.

Unlike the multiple series of vias shown in FIG. 11, where the firstseries and the second series are electrically isolated from each other,the series defined by PTH vias 1504 is electrically connected to theseries defined by PTH vias 1510. Thus, during the selective removalblock 310 of the flowchart of FIG. 3, all portions of the conductivematerial existing between the two series are removed from the surfacesof the dielectric board, except for the linking portion 1514. Becausethe series are not electrically isolated, they provide an inductivefilter to only a single phase of supplied current.

By allowing the current to travel in parallel along two series ofinterconnected PTH vias, the cross-sectional area of traces and PTH viasis effectively doubled. This larger cross-sectional area provides lessresistance, and thus the value of resistor 902 (FIG. 9) is essentiallyreduced. Although only two series of interconnected PTH vias are shownto be connected by linking portion 1514 in FIG. 15, more series ofinterconnected PTH vias could be electrically connected by additionallinking portions in other embodiments, thus reducing the effectiveresistance even further.

FIG. 16 illustrates a top view of a low-resistance, single-phase,coil-type inductive filter in accordance with one embodiment of thepresent invention. The principle behind the structure shown in FIG. 16is the same as that shown in FIG. 15, except that two coil-typeinductive structures are electrically connected by linking portion 1602.The first inductive structure is defined by traces 1604 and PTH vias1606, and the second structure is defined by traces 1608 and PTH vias1610. As with the structure described in conjunction with FIG. 15, moreseries of PTH vias could be electrically connected by additional linkingportions in other embodiments in order to reduce the effectiveresistance of the inductive filter.

The low-resistance structures illustrated in FIGS. 15 and 16 could alsobe used in multiphase applications. FIG. 17 illustrates a top view of alow-resistance, multi-phase, collinear inductive filter in accordancewith one embodiment of the present invention. The filter consists of twosets of series of interconnected PTH vias. Each set is a subset of allthe series of interconnected PTH vias, and each set is electricallyisolated from the other sets. The first set is defined by linkingportion 1702, a first series of interconnected PTH vias consisting oftraces 1704 and PTH vias 1706, and a second series of interconnected PTHvias consisting of traces 1708 and PTH vias 1710. The second set, whichis electrically isolated from the first set, is defined by linkingportion 1712, a third series of interconnected PTH vias consisting oftraces 1714 and PTH vias 1716, and a fourth series of interconnected PTHvias consisting of traces 1718 and PTH vias 1720.

A first phase of current could be carried by the first set, and a secondphase could be carried by the second set. This is similar to themulti-phase structure shown in FIG. 11, except that each phase iscarried by a PTH structure having a reduced resistance. In alternateembodiments, more series of interconnected vias could be included withineach set, and more sets could be provided to carry additional phases ofcurrent.

The multi-phase, low-resistance approach also could apply to thecoil-type via structures. FIG. 18 illustrates a top view of alow-resistance, multi-phase, coil-type inductive filter in accordancewith one embodiment of the present invention. The filter consists of twosets of series of interconnected PTH vias. The first set is defined bylinking portion 1802, a first series of interconnected PTH viasconsisting of traces 1804 and PTH vias 1806, and a second series ofinterconnected PTH vias consisting of traces 1808 and PTH vias 1810. Thesecond set, which is electrically isolated from the first set, isdefined by linking portion 1812, a third series of interconnected PTHvias consisting of traces 1814 and PTH vias 1816, and a fourth series ofinterconnected PTH vias consisting of traces 1818 and PTH vias 1820.

As with the structure illustrated in FIG. 17, a first phase of currentcould be carried by the first set, and a second phase could be carriedby the second set. This is similar to the multiphase structure shown inFIG. 14, except that each phase is carried by a PTH structure having areduced resistance. In alternate embodiments, more series ofinterconnected vias could be included within each set, and more setscould be provided to carry additional phases of current.

The inductive properties of the embedded filter structures describedabove can be enhanced by providing a ferromagnetic material embeddedwithin the dielectric board. FIG. 19 illustrates a flowchart of a methodfor providing a dielectric board (see block 302, FIG. 3) with anembedded ferromagnetic material pattern in accordance with oneembodiment of the present invention. The method of FIG. 19 should beviewed in conjunction with FIGS. 20–29, which are schematic crosssections and top views illustrating various stages of fabricating anembedded filter or transformer in accordance with one embodiment of thepresent invention.

The method begins, in block 1902, by providing a first dielectricmaterial layer (2002, FIG. 20). The dielectric material layer has a topsurface 2004 and a bottom surface 2006, and can consist of a materialthat is the same as the materials discussed in conjunction with block302 of FIG. 3. In various embodiments, the thickness of first dielectricmaterial layer 2002 is within a range of 300–500 microns, with it beingapproximately 400 microns in one embodiment. First dielectric materiallayer 2002 could be thicker or thinner than this range in otherembodiments.

In block 1904, a ferromagnetic material pattern (2102, FIG. 21) isdeposited on the top surface 2004. In one embodiment, the ferromagneticmaterial pattern 2102 is deposited using an electrolytic plating andetching process. In another embodiment, pattern 2102 is deposited usinga photoimaging technique. In various embodiments, the thickness offerromagnetic material pattern 2102 is within a range of 5–50 microns,with it being approximately 30 microns in one embodiment. Ferromagneticmaterial pattern 2102 could be thicker or thinner than this range inother embodiments.

The ferromagnetic material used to create pattern 2102 can be selected,in part, based on the magnetic permeability of the material. Onematerial that could be used, for example, is silicon-iron, althoughother magnetic materials could be used in other embodiments.

The ferromagnetic material pattern can take any of a number of shapes,and can have a range of widths. For example, FIG. 22 illustrates a topview of dielectric material layer 2002 upon which a ferromagneticmaterial strip 2202 is deposited. FIG. 23, on the other hand,illustrates a top view of dielectric material layer 2002 upon which arectangular ferromagnetic pattern 2302 is deposited. This pattern can beused, for example, as a core of a transformer structure, as will bedescribed in detail in conjunction with FIG. 33, although otherclosed-ended shapes, such as an oval or circle, also could be used toprovide a transformer core.

Referring back to FIG. 19, a second dielectric material layer (2402,FIG. 24) is then applied to the top surface 2004 of the first dielectricmaterial layer 2002 over the ferromagnetic material pattern 2102. In oneembodiment, second dielectric material layer 2402 is laminated to firstdielectric material layer 2002. In various embodiments, the thickness ofsecond dielectric material layer 2402 is within a range of 300–500microns, with it being approximately 400 microns in one embodiment.Second dielectric material layer 2402 could be thicker or thinner thanthis range in other embodiments.

After the second dielectric material layer 2402 is applied, the methodof fabricating the interconnect structures in accordance with variousembodiments of the present invention follows the procedure described inFIG. 3. Specifically, in block 304, one or more series of holes (2502,2504, FIG. 25) are formed through the dielectric board. These holes areillustrated in the cross-sectional view of FIG. 25 as being formed onone side or the other of the ferromagnetic material pattern 2102. Inother words, holes 2502 are formed on a first side of ferromagneticmaterial pattern 2102, and holes 2504 are formed on the other side offerromagnetic material pattern 2102.

This is further illustrated in FIG. 26, which is a top view of thedielectric board having a ferromagnetic material pattern 2102 embeddedtherein. Holes 2502 are positioned along line 2604 on one side offerromagnetic material pattern 2102. Holes 2504 are positioned alongline 2606 on the other side of ferromagnetic material pattern 2102.

Referring again to FIG. 3, after forming one or more series of holes,blocks 306, 308, and 310 are performed. These include the procedures,described previously, of plating the holes and the top and bottomsurfaces, filling the holes with a conductive or non-conductivematerial, and selectively removing portions of the conductive materialon the top and bottom surfaces.

The result of this procedure is illustrated in FIG. 27, whichillustrates a schematic cross section of a structure that includes aseries of interconnected PTH vias in accordance with one embodiment. Asdescribed previously, the filled PTH vias 2702 are located on both sidesof the embedded ferromagnetic material pattern 2102. The conductivetraces 2704 on the top and bottom surfaces of the dielectric boardprovide electrical connections between adjacent PTH vias. Thus, thetraces 2704 and vias 2702 form a coil-like inductive structure having aferromagnetic strip embedded in the center of the coil.

FIG. 28 illustrates a top view of a single-phase, coil-type inductivefilter 2800 with a ferromagnetic core in accordance with one embodimentof the present invention. The structure of traces 2802 and PTH vias 2804is similar to the structure described in conjunction with FIG. 13,except that an embedded ferromagnetic pattern 2806 is deposited throughthe center of the coil-like structure.

The single-phase, coil-type inductive filter structure 2800 shown inFIG. 28 could form a part of various other embodiments of inductivefilters. For example, in one embodiment, multiple structures 2800 couldbe provided to form a multi-phase, coil-type inductive filter similar tothat described in conjunction with FIG. 14, except where each series ofPTH vias coils around a ferromagnetic core. In another embodiment,multiple structures 2800 could be provided and electrically connected bya linking portion to provide a low-resistance, single-phase, coil-typeinductive filter similar to that described in conjunction with FIG. 16,except where each series of PTH vias coils around a ferromagnetic core.Finally, in another embodiment, multiple structures 2800 could beprovided to form a low-resistance, multi-phase, coil-type inductivefilter similar to that described in conjunction with FIG. 17, exceptwhere each series of PTH vias coils around a ferromagnetic core.

As explained previously, the interconnected PTH via structure could alsobe used to form an embedded transformer structure. Basically, this isdone by providing a dielectric board with an embedded ferromagnetic corehaving a closed-ended pattern, such as a rectangle, square, circle, oroval, for example. The method of FIG. 3 is then performed to produce twointerconnected via structures coiled around the core.

FIG. 29 illustrates a top view of a transformer in accordance with oneembodiment of the present invention. The transformer includes two seriesof interconnected PTH vias, each having a coil-type inductor structure.

A first series includes PTH vias 2902 that are interconnected by traces2904 on the top and bottom surfaces of dielectric board 2906. A secondseries includes PTH vias 2908 that are interconnected by traces 2910 onthe top and bottom surfaces of dielectric board 2906. A ferromagneticcore 2912 is embedded in dielectric board 2906. The coils formed by boththe first and second series of PTH vias wind around core 2912. Core 2912is shown having a rectangular pattern in FIG. 29. In other embodiments,other closed-ended shapes also could be used.

In accordance with standard transformer behavior, when current isapplied to the first series of PTH vias 2902, a current is induced inthe second series 2908. Because the number of coils in the first seriesis different from the number of coils in the second series, the inducedoutput voltage, Vout, between leads 2914 of the second series will bedifferent from the input voltage, Vin, between leads 2916 of the firstseries. In alternate embodiments, the voltage difference also could beachieved using geometrically different coil configurations. AlthoughFIG. 29 illustrates four coils in the first series, and two and a halfcoils in the second series, more or fewer coils could be included ineither series. In addition, the dimensions of the coils could be varied,for example, by adjusting the distances and angles between adjacent PTHvias.

FIG. 30 illustrates an electrical circuit that simulates the electricalcharacteristics of the transformer illustrated in FIG. 29. The circuitincludes a transformer 2902 having a first coil 2904 and a second coil2906. The voltage, Vin, applied across the first coil 2904 istransformed to a different voltage, Vout, across the second coil 2906.

Embedded inductive filters and/or transformers such as those shown inFIGS. 10, 11, 13–18, 28, and 29 could be used in many applications wherea filter or transformer is needed, but where it is desirable not to usea discrete device. In addition, embedded inductive filters and/ortransformers could be used in many applications where it is desirable toplace a filter or transformer on an IC package, interposer or PC board.

FIG. 31 illustrates the incorporation of one or more embedded series ofinterconnected PTH vias 3102 in an IC package 3104 in accordance withone embodiment of the present invention. Starting from the top of FIG.31, an integrated circuit 3106 is housed by IC package 3104. Integratedcircuit 3106 contains one or more circuits which are electricallyconnected to IC package 3104 by connectors 3108. One or more of thesecircuits act as loads (e.g., load 122, FIG. 1) to which power issupplied by VRM 3110.

Integrated circuit 3106 could be any of a number of types of integratedcircuits. In one embodiment of the present invention, integrated circuit3106 is an microprocessor, although integrated circuit 3106 could beother devices in other embodiments. In the example shown, integratedcircuit 3106 is a “flip chip” type of integrated circuit, meaning thatthe input/output terminations on the chip can occur at any point on itssurface. After the chip has been readied for attachment to IC package3104, it is flipped over and attached, via solder bumps or balls 3108 tomatching pads on the top surface 3114 of IC package 3104. Alternatively,integrated circuit 3106 could be a surface mount chip, whereinput/output terminations are connected to IC package 3104 using bondwires to pads on the top surface 3114 of IC package 3104.

IC package 3104 is coupled to a socket 3116 on a PC board 3118. In theexample shown, IC package 3104 includes pins 3120 that mate withcomplementary pin holes in socket 3116. Alternatively, IC package 3104could be electrically and physically connected to PC board 3118 usingsolder connections, such as ball grid array connections, for example.

PC board 3118 could be, for example, a mother board of a computersystem. As such, it acts as a vehicle to supply power to VRM 3110 and,thus, integrated circuit 3106. This power is supplied through traces(not shown) on PC board 3118, socket 3116, pins 3118, and traces (notshown) on IC package 3104.

In one embodiment, PC board 3118 supplies AC power to VRM 3110. In someinstances, VRM 3110 must transform the AC power to DC power beforesupplying that power to integrated circuit 3106. As described inconjunction with FIG. 1, AC power is transformed to DC power, in part,using a voltage transformer (e.g., transformer 112, FIG. 1). Inaccordance with one embodiment of the present invention, thattransformer is supplied by two or more embedded series of interconnectedPTH vias 3102. The fabrication and structure of this embeddedtransformer were described in detail in conjunction with FIGS. 19-30. Inanother embodiment, the transformer could be part of VRM 3110.

As also described previously, after the supply voltage has beenregulated by VRM 3110, the voltage is filtered using an inductivefilter, and supplied to integrated circuit 3106 through connectors 3108.In accordance with one embodiment of the present invention, theinductive filter is provided by one or more embedded series ofinterconnected PTH vias 3102. The fabrication and structure of thisembedded inductive filter were described in detail in conjunction withFIGS. 9–28.

By providing an embedded inductive filter 3102, the discretecomponent-type inductive filter of the prior art can be eliminated orsubstantially reduced in size. This enables the VRM to be placed on theIC package 3104 and, thus, much closer to integrated circuit 3106. Theproximity of the VRM to integrated circuit 3106 results in a smallervoltage drop than is possible using prior art methods of placing the VRMon PC board 3118. In addition, cost saving are achieved, because thediscrete component filter is eliminated or reduced in size.

By providing an embedded transformer 3102, the transformer typicallyincluded in the VRM in prior art systems can be removed from the VRM.Thus, the size of the VRM can be reduced, further facilitating theplacement of the VRM on the IC package 3104. From the above description,it should be apparent that the embedded series of interconnected PTHvias 3102 can be used for either an embedded transformer, an embeddedinductive filter, or both.

As explained previously, integrated circuit packages are sometimesconnected to a PC board through an interposer, which acts as adimensional interface between IC package connectors and connectors onthe PC board. When an interposer is present, the VRM and/or the seriesof interconnected PTH vias can be moved onto the interposer.

FIG. 32 illustrates the incorporation of one or more embedded series ofinterconnected PTH vias 3202, 3204 in an interposer 3206 and/or ICpackage 3208 in accordance with one embodiment of the present invention.Interposer 3206 is present between IC package 3208 and PC board 3210. ICpackage 3208 could be connected to interposer 3206 using solderconnections 3212 or pin connections. Similarly, interposer 3206 could beconnected to PC board 3210 using pin connections 3214 or solderconnections.

VRM 3216 is located on interposer 3206. Similar to the embodimentdepicted in FIG. 31, two or more series of interconnected PTH vias 3202could serve as a transformer of power supplied to VRM 3216 from PC board3210. One or more series of interconnected PTH vias 3202 also couldserve as an inductive filter between VRM 3216 and integrated circuit3218.

In one embodiment, an additional inductive filter 3204 is located on theIC package 3208, as well. If the inductive filter is provided byinterconnected PTH vias on both the interposer 3206 and the IC package3208, a circuit diagram of the filter would resemble two inductorsconnected in series between VRM 3216 and the integrated circuit 3218. Inalternate embodiments, the entire inductive filter is located on eitherIC package 3208 or interposer 3206.

The IC packages and interposer described in conjunction with FIGS. 31and 32 could be connected to a PC board forming part of a generalpurpose computer system. FIG. 33 illustrates a general purpose computersystem 3300 that includes an embedded inductive filter and/ortransformer in accordance with various embodiments of the presentinvention.

Computer system 3300 is housed on PC board 3302, and includes bus 3308,microprocessor 3304, package 3306, power supply signal generator 3310,and memory 3312. Package and/or interposer 3306 couples microprocessor3304 to bus 3308 in order to communicate power supply signals andnon-power supply signals between microprocessor 3304 and devices coupledto bus 3308. For the embodiment of the present invention shown in FIG.33, bus 3308 couples microprocessor 3304 to memory 3312 and power supplysignal generator 3310. However, it is to be understood that inalternative embodiments of the present invention, microprocessor 3304can be coupled to memory 3312 and power supply signal generator 3310through two different busses. In addition, in alternative embodiments ofthe present invention, power supply signal generator 3310 is notpositioned on PC board 3302, but instead is positioned elsewhere.

Thus, various embodiments of an interconnected PTH via structure andmethods of fabricating that structure have been described, along with adescription of the incorporation of a package and/or interposer thatincludes that structure on a PC board within a general purpose computersystem.

The method and apparatus of the present invention provide a circuitconfiguration having a VRM closer to the integrated circuit than ispossible using prior art methods and apparatuses. This is accomplishedwithout requiring a substantially larger interposer or IC package. Inaddition, use of the method and apparatus of the present inventionresults in a reduction in the amount of surface area required by a VRMor its associated inductive filter.

CONCLUSION

Embodiments of the present invention provide an embedded inductivefilter and an embedded transformer that can be used in place of variousdiscrete components on an integrated circuit package, interposer orprinted circuit board.

In the foregoing detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which are shown by way of illustration specific preferredembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention.

It will be appreciated by those of ordinary skill in the art that anyarrangement which is calculated to achieve the same purpose may besubstituted for the specific embodiment shown. For example, illustrativeembodiments describe vias between two levels of interconnect. However,those skilled in the art will recognize that many interconnect levelsmay be connected by vias in accordance with the present invention.

The present invention has been described in the context of providing anembedded inductive filter or transformer in a VRM application. One ofordinary skill in the art would understand, based on the descriptionherein, that the method and apparatus of the present invention couldalso be applied in many other applications where an embedded inductivefilter or transformer are desired. Therefore, all such applications areintended to fall within the spirit and scope of the present invention.

In addition, the terms “chip,” “integrated circuit,” “monolithicdevice,” “semiconductor device,” and “microelectronic device” are oftenused interchangeably in this field. The present invention is applicableto all the above as they are generally understood in the field.

This application is intended to cover any adaptations or variations ofthe present invention. The foregoing detailed description is, therefore,not to be taken in a limiting sense, and it will be readily understoodby those skilled in the art that various other changes in the details,materials, and arrangements of the parts and steps which have beendescribed and illustrated in order to explain the nature of thisinvention may be made without departing from the spirit and scope of theinvention as expressed in the adjoining claims.

1. An inductive filter comprising: a dielectric board having a topsurface and a bottom surface; a series of plated through hole (PTH) viasformed in the dielectric board; conductive material traces on the topsurface and the bottom surface that electrically connect the PTH vias,wherein adjacent PTH vias are electrically connected by a trace oneither the top surface or the bottom surface, and wherein the adjacentPTH vias in the series alternate between being electrically connected bya trace on the top surface or electrically connected by a trace on thebottom surface; at least one additional series of PTH vias formed in thedielectric board; and additional conductive material traces on the topsurface and the bottom surface that electrically connect each of the PTHvias in the at least one additional series, wherein adjacent PTH vias inthe at least one additional series alternate between being electricallyconnected by traces on the top surface or the bottom surface.
 2. Theinductive filter as claimed in claim 1, wherein the dielectric boardcomprises a ferromagnetic material pattern embedded therein.
 3. Theinductive filter series as claimed in claim 1, wherein the PTH vias arefilled with a conductive material.
 4. The inductive filter as claimed inclaim 1, wherein the PTH vias in the series and in the additional seriesare substantially collinear.
 5. The inductive filter as claimed in claim1, wherein the series and the additional series of PTH vias each form acoil-like structure.
 6. The inductive filter as claimed in claim 5,wherein the dielectric board comprises an embedded ferromagneticmaterial pattern, and each of the coil-like structures winds around theembedded ferromagnetic material pattern.
 7. The inductive filter asclaimed in claim 1, wherein the first series is electrically isolatedfrom the at least one additional series.
 8. The inductive filter asclaimed in claim 1, wherein a linking portion of conductive materialelectrically connects at least one PTH via in each of the first seriesand the at least one additional series.